Crystal oscillator device and method of measuring crystal oscillator characteristic

ABSTRACT

A crystal oscillator device is disclosed. The crystal oscillator device includes a crystal piece provided in a casing; a pair of excitation electrodes provided for the crystal piece; a coil provided on the crystal piece; a magnetic flux generating member configured to generate magnetic flux passing through the coil; and an alarm generator configured to generate an alarm based on a signal whose amplitude is equal to or less than a reference value, the signal being generated in the coil.

CROSS-REFERENCE TO RELATED APPLICATIONS

This present application is based upon and claims the benefit ofpriority of the prior Japanese Patent Application No. 2016-116460, filedon Jun. 10, 2016, the entire contents of which are incorporated hereinby reference.

FIELD

The present disclosure relates to a crystal oscillator device and amethod of measuring a characteristic of a crystal oscillator.

BACKGROUND

With respect to an oscillator using a MEMS (Micro Electro MechanicalSystems) resonator, a technique is known in which an oscillation outputcoil surrounding a wiring in an oscillation circuit in a noncontactmanner is provided and an oscillation output is taken out from theoscillation output coil via a buffer amplifier.

[Patent Document 1] Japanese Laid-open Patent Publication No. 2012-70193

[Patent Document 2] Japanese Laid-open Patent Publication No.2004-198126

However, according to the conventional technique as described above, itis difficult to detect a state of the crystal oscillator before atransition to an output stop state (for example, clock stop) based onthe output of the buffer amplifier. It is noted that the output stop ofthe crystal oscillator may occur suddenly due to abnormality of thecrystal oscillator or the like.

SUMMARY

According to one aspect of the disclosure, a crystal oscillator deviceis provided, which includes: a crystal piece provided in a casing; apair of excitation electrodes provided for the crystal piece; a coilprovided on the crystal piece; a magnetic flux generating memberconfigured to generate magnetic flux passing through the coil; and analarm generator configured to generate an alarm based on a signal whoseamplitude is equal to or less than a reference value, the signal beinggenerated in the coil.

The object and advantages of the embodiment will be realized andattained by means of the elements and combinations particularly pointedout in the claims. It is to be understood that both the foregoinggeneral description and the following detailed description are exemplaryand explanatory and are not restrictive of the invention.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a top view schematically illustrating a configuration of acrystal oscillator according to a first embodiment.

FIG. 1B is a cross-sectional view along a line B-B in FIG. 1A.

FIG. 2 is a diagram explaining an example of coil implementation.

FIG. 3A is an explanatory diagram of a principle in which a currentflows in a coil due to oscillation of a crystal oscillator device.

FIG. 3B is an explanatory diagram of a principle in which a currentflows in a coil due to oscillation of a crystal oscillator device.

FIG. 3C is an explanatory diagram of a signal waveform appearing in acoil.

FIG. 3D is an explanatory diagram of a signal waveform appearing in acoil.

FIG. 4 is a diagram schematically illustrating an example of a circuitconfiguration of a crystal oscillator device including a crystaloscillator and an IC.

FIG. 5 is a diagram for illustrating an example of an invertingamplifier.

FIG. 6 is an explanatory diagram of characteristics in a case where thecrystal oscillator is a normal product.

FIG. 7 is an explanatory diagram of an output stop event of the crystaloscillator due to abnormality.

FIG. 8A is a diagram illustrating a time-series waveform of a signalappearing at a point A in the case of an abnormal product.

FIG. 8B is a diagram illustrating a time-series waveform of a signalappearing at a point B in the case of an abnormal product.

FIG. 8C is a diagram illustrating a time-series waveform of a signalappearing at a point C in the case of an abnormal product.

FIG. 8D is a diagram illustrating a time-series waveform of a signalappearing in the coil in the case of an abnormal product.

FIG. 9 is a diagram explaining an example of an operation according tothe first embodiment.

FIG. 10A is a diagram explaining another example of implementation of amagnet.

FIG. 10B is a diagram explaining another example of implementation of amagnet.

FIG. 10C is a diagram explaining another example of implementation of amagnetic flux generating member other than a magnet.

FIG. 11 is a diagram explaining an example of coil implementationaccording to a second embodiment.

FIG. 12 is a diagram illustrating a cross-sectional view along a lineD-D in FIG. 11.

FIG. 13 is a schematic cross-sectional view of a crystal oscillatoraccording to a second embodiment.

FIG. 14 is a diagram explaining an example of coil implementationaccording to a third embodiment.

FIG. 15 is a diagram illustrating a cross-sectional view along a lineE-E in FIG. 14.

FIG. 16 is a diagram explaining an example of magnet implementation.

FIG. 17A is a diagram explaining a variant of the third embodiment.

FIG. 17B is a diagram explaining a variant of the third embodiment.

DESCRIPTION OF EMBODIMENTS

In the following, embodiments are described in detail with reference toappended drawings.

First Embodiment

FIG. 1A is a top view schematically illustrating a configuration of acrystal oscillator 100 according to a first embodiment, and FIG. 1B is across-sectional view along a line B-B in FIG. 1A. FIG. 2 is a diagramexplaining an example of implementation of a coil 50, and a two-sideview (plan views illustrating an upper surface and a lower surface) of acrystal piece 10. In FIG. 1A, a lid of a casing 30 is not illustrated sothat an inside can be seen, and invisible elements (an externalelectrode 41, etc.) are indicated by broken lines. In addition, in FIG.1A, only an outline of the crystal piece 10 is indicated by an alternatelong and short dash line (the coil 50, etc., are not illustrated). It isnoted that FIGS. 1A and 1B illustrate an IC 200 in addition to thecrystal oscillator 100. Also, in FIG. 1B, a polarity (N pole, S pole) ofa magnet 59 is schematically illustrated as “N” and “S”.

Hereinafter, a thickness direction of the crystal piece (crystal blank)10 (vertical direction in FIG. 1B) is defined as the vertical direction,and the side of the casing 30 having the lid is referred to as “upperside”. However, an orientation of the installation of the crystaloscillator 100 is arbitrary. In the following, an “outer surface” refersto a surface exposed to an outside of the casing 30, and an “innersurface” refers to a surface exposed to an inner space of the casing 30.Further, as illustrated in FIG. 1A, an X direction is defined as adirection corresponding to a direction of a main vibration (thicknessshear vibration) direction of the crystal oscillator 100.

The crystal oscillator 100 includes a crystal piece 10, excitationelectrodes 20, a casing 30, external electrodes 41 to 44, a coil 50, anda magnet (an example of a magnetic flux generating member). Asillustrated in FIGS. 1A and 1B, the crystal oscillator 100 is of asurface mounting type.

The crystal piece 10 may be, for example, an AT-cut artificial quartzcrystal substrate. An outer shape of the crystal piece 10 is arbitrary,and in the first embodiment, it is a rectangle, but other shapes may beused. The supporting structure of the crystal piece 10 is arbitrary. Forexample, the crystal piece 10 may be supported by the casing 30 in acantilever structure. In the example illustrated in FIGS. 1A and 1B, thecrystal piece 10 is supported in a cantilever structure on a bankportion 31 of the casing 30. When the crystal oscillator 100 is driven,the crystal piece vibrates in the X direction (thickness shearvibration).

The excitation electrodes 20 excite the crystal piece 10. The excitationelectrodes 20 include an upper excitation electrode 21 provided on theupper surface of the crystal piece 10 and a lower excitation electrode22 provided on the lower surface of the crystal piece 10. The excitationelectrodes 20 excite the crystal piece 10 by a potential differencebetween the upper excitation electrode 21 and the lower excitationelectrode 22. It is noted that the excitation electrodes 20 may be madeof gold, silver, aluminum, or the like.

The excitation electrodes 20 are electrically connected to an IC(Integrated Circuit) 200. The way of electrically connecting theexcitation electrodes 20 and the IC 200 is arbitrary. In the exampleillustrated in FIGS. 1A and 2, the upper excitation electrode 21 iselectrically connected to the IC 200 via a conductive pattern 47 (seeFIG. 2) formed on an upper surface of the crystal piece 10, anelectrically conductive adhesive 49, a conductive pattern 471 formed onan inner surface of a lower part of the casing 30, and a wire 473.Further, the lower excitation electrode 22 is electrically connected tothe IC 200 via a conductive pattern 48 (see FIG. 2) formed on a lowersurface of the crystal piece 10, an electrically conductive adhesive49B, a conductive pattern 481 formed on an inner surface of a lower partof the casing 30, and a wire 483. It is noted that the wires 473 and 483(the same applies to a wire 493, etc., described hereinafter) may beformed by wire bonding. It is noted that the electrically conductiveadhesives 49, 49B (as well as conductive adhesives 49A, 49C describedhereinafter) may be provided at an edge portion of the crystal piece 10(i.e., the edge on the cantilevered side).

The casing 30 accommodates the crystal piece 10. The casing 30 is madeof, for example, a ceramic material. In this case, the casing 30 may be,for example, a ceramic package formed by laminating ceramic materiallayers. The casing 30 includes a lid 34 (see FIG. 1B and the like), andhermetically encloses the crystal piece 10 in an internal space (cavity)thereof. For example, the internal space of the casing 30 is undervacuum or filled with dry nitrogen and sealed with the lid 34. It isnoted that the lid 34 may be a metal plate or a ceramic plate.

The external electrodes 41 to 44 are provided on the casing 30. In theexample illustrated in FIGS. 1A and 1B, the external electrodes 41 to 44are provided on an outer surface of the lower portion of the casing 30.The external electrodes 41 to 44 may be electrically connected to the IC200. The way of electrically connecting the external electrodes 41 to 44and the IC 200 is arbitrary. In the example illustrated in FIGS. 1A and1B, the external electrode 41 is electrically connected to the IC 200via a conductive pattern 411 formed on the outer surface of the lowerportion of the casing 30, a via 412 formed in the casing 30, and a wire413. Similarly, the external electrode 44 is electrically connected tothe IC 200 via a conductive pattern 441 formed on the outer surface ofthe lower portion of the casing 30, a via 442 formed in the casing 30,and a wire 443. Although not illustrated, the external electrodes 42, 43and the IC 200 may also be electrically connected via a conductivepattern or the like in the same manner.

The external electrodes 41 to 44 may be electrically connected to anexternal device or the like outside of the casing 30. That is, theexternal electrodes 41 to 44 are electrically connected to the IC 200and the external device to electrically connect the IC 200 to theexternal device or the like. In the example illustrated in FIGS. 1A and1B, the external electrodes 41 and 44 may be used to extract signalsfrom an alarm output terminal 222 and a clock output terminal 220 (seeFIG. 4) of the IC 200. Further, in the example illustrated in FIGS. 1Aand 1B, the external electrodes 42, 43 may be used for electricallyconnecting the IC 200 to ground and a power supply (both notillustrated) (wirings are not illustrated).

The coil 50 and the magnet 59 are provided in the crystal oscillator 100such that the density of the magnetic flux passing through the coil 50and generated from the magnet 59 changes in accordance with theoscillation of the crystal oscillator 100. The coil 50 is electricallyconnected to the IC 200. The way of electrically connecting the coil 50and the IC 200 is arbitrary. The electrical connection between the coil50 and the IC 200 may be implemented by, for example, wire bonding orthe like.

In the example illustrated in FIGS. 1A and 2, the coil 50 includes coilpattern portions 511 and 521, wiring portions 512 and 522, and a throughhole 56. The coil pattern portions 511 and 521 are formed on the uppersurface and the lower surface of the crystal piece 10, respectively. Thecoil pattern portions 511 and 521 are spirally formed from the throughhole 56 in a plurality of turns in a plan view (a view in a directionperpendicular to the surface of the crystal piece 10). The coil patternportions 511 and 521 are wound in the same direction. One end (thecenter side of the turns) of each of the coil pattern portions 511 and521 is electrically connected to the other through the through hole 56.It is noted that the through hole 56 can be formed by etching thecrystal piece 10. The other ends of the coil pattern portions 511 and521 are electrically connected to the electrode 52 and the electrode 54via the wiring portions 512 and 522, respectively. The wiring portions512 and 522 are formed on the upper surface and the lower surface of thecrystal piece 10, respectively. As illustrated in FIG. 1A, the electrode52 is electrically connected to the IC 200 via an electricallyconductive adhesive 49C, a conductive pattern 461 formed on the innersurface of the lower portion of the casing 30, and a wire 463.Accordingly, one end of the coil 50 is electrically connected to the IC200 via the electrode 52, the conductive adhesive 49C, the conductivepattern 461, and the wire 463. As illustrated in FIG. 1A, the electrode54 is electrically connected to the IC 200 via an electricallyconductive adhesive 49A, a conductive pattern 491 formed on the innersurface of the lower portion of the casing 30, and a wire 493.Accordingly, the other end of the coil 50 is electrically connected tothe IC 200 via the electrode 54, the conductive adhesive 49A, theconductive pattern 491, and the wire 493.

Further, in the example illustrated in FIGS. 1A and 2, the magnet 59 isprovided such that the magnet 59 also functions as the lid 34. However,the magnet 59 may be provided in a part of the lid 34 (for example, onlyin a region overlapping with the coil pattern portions 511 and 521 in atop view) or a magnetic flux generating material (for example, a magnetmaterial) is applied to the lid 34. The magnet 59 is provided in aregion overlapping with the coil 50 in a plan view (a view in adirection perpendicular to the surface of the crystal piece 10). Themagnet 59 may be provided at a position where the density of themagnetic flux passing through the coil 50 is maximum in the neutralstate (for example, in a state of not oscillating) of the crystal piece10. It is noted that either of the N pole and the S pole in the magnet59 may be on the upper side.

In the examples illustrated in FIGS. 1A and 2, the coil 50 is formed onboth the upper surface and the lower surface of the crystal piece 10 inorder to increase the number of turns; however, the coil 50 may beformed on only one of the upper surface and the lower surface of thecrystal piece 10. Further, in the examples illustrated in FIGS. 1A and2, the coil pattern portions 511 and 521 are formed in a plurality ofturns in order to increase the number of windings, but may be woundonce. Further, in the examples illustrated in FIGS. 1A and 2, the coilpattern portions 511 and 521 are provided on the farther side from thebank portion 31 in the X direction with respect to the excitationelectrodes 20 (i.e., the free end side of the crystal piece 10);however, the coil pattern portions 511 and 521 may be provided at anarbitrary position with respect to the excitation electrodes 20. Forexample, the coil pattern portions 511 and 521 may be provided on theside closer to the bank portion 31 in the X direction with respect tothe excitation electrodes 20.

When the crystal oscillator 100 is in the oscillation state, the crystalpiece 10 is subjected to thickness shear vibration (also referred to as“main vibration”), and the density of the magnetic flux passing throughthe coil 50 changes according to the oscillation of the crystal piece10. Therefore, due to electromagnetic induction, a voltage waveformoscillating at a cycle corresponding to an output frequency of thecrystal oscillator 100 is generated between the opposite ends of thecoil 50. Specifically, during the thickness shear vibration, the coil 50is displaced in one direction (parallel to the X direction) from thecenter position of the thickness shear vibration of the crystal piece 10in FIG. 3A (see arrow R 2). At this time, since the position of the coil50 with respect to the magnet 59 changes in a direction such that thedensity of the magnetic flux passing through the coil 50 decreases,current I flows in a direction to increase the density of the magneticflux through the coil 50. On the other hand, the coil 50 is displaced inthe other direction (see arrow R 4) from the maximum displacementposition of the thickness shear vibration of the crystal piece 10illustrated in FIG. 3B. At this time, since the position of the coil 50with respect to the magnet 59 changes in a direction such that thedensity of the magnetic flux passing through the coil 50 increases,current I flows in a direction (i.e., an opposite direction with respectto the direction illustrated in FIG. 3A) to decrease the density of themagnetic flux through the coil 50. In this way, the voltage waveformoscillating at the cycle corresponding to the output frequency of thecrystal oscillator 100 is generated between the opposite ends of thecoil 50. As illustrated in FIGS. 3C and 3D, the frequency and theamplitude of the voltage waveform generated between the opposite ends ofthe coil 50 decrease as an oscillation level of the crystal oscillator100 decreases. This is because, with respect to the amplitude, theamount of change in the density of the magnetic flux passing through thecoil decreases as the oscillation level of the crystal oscillator 100decreases. FIGS. 3C and 3D are explanatory diagrams of voltage waveforms(time-series waveforms of signals appearing in the coil 50) appearingacross the coil 50 in the crystal oscillator 100 in the oscillationstate. FIG. 3C illustrates a waveform in the case where the oscillationlevel of the crystal oscillator 100 is in a normal state and FIG. 3Dillustrates a waveform in the case where the oscillation level of thecrystal oscillator 100 is lowered. For example, in the exampleillustrated in FIGS. 3C and 3D, when the oscillation level of thecrystal oscillator 100 transitions from a normal state to a reducedstate, the wavelength is lengthened from λ to λ′ (that is, the outputfrequency is lowered), and the amplitude is decreased from Am 1/2 to Am1′/2.

As described above, the IC 200 is electrically connected to theexcitation electrodes 20 and the coil 50 of the crystal oscillator 100.The IC 200 forms an example of a crystal oscillator device together withthe crystal oscillator 100. In the example illustrated in FIGS. 1A and1B, the IC 200 is provided on an inner surface of the lower portion ofthe casing 30. That is, the IC 200 is provided in the internal space ofthe casing 30. However, in the modified example, the IC 200 may beprovided outside the casing 30. In this case, for example, theexcitation electrodes 20, the coil 50, and the magnet may beelectrically connected to the external electrodes 41 to 44,respectively, and the IC 200 may be electrically connected to theexternal electrodes 41 to 44.

It is noted that, in the examples illustrated in FIGS. 1A and 1B, the IC200 may be provided with bumps (terminals) on the bottom surfacethereof. In this case, the IC 200 may be electrically connected to thevia 412 or the like via the bumps instead of the wire 413 or the like.

FIG. 4 is a diagram schematically illustrating an example of a circuitconfiguration of the crystal oscillator 100 and the IC 200. In FIG. 4,with respect to IC 200, capacitors of terminals, stray capacitance ofwiring patterns of the printed circuit board, resistance for limitingthe current (see arrow i in FIG. 4) flowing through the crystaloscillator 100, etc., are not illustrated.

In the example illustrated in FIG. 4, the upper excitation electrode 21and the lower excitation electrode 22 of the crystal oscillator 100 areelectrically connected to an input terminal 202 and an output terminal204 of the IC 200, respectively. However, the lower excitation electrode22 and the upper excitation electrode 21 of the crystal oscillator 100may be connected to the input terminal 202 and the output terminal 204of the IC 200, respectively. The crystal oscillator 100 cooperates withthe IC 200 to generate a clock (reference clock) used in an arbitrarydevice (for example, a communication control device such as a basestation device or a relay station device).

A matching capacitor 300 is electrically connected to the crystaloscillator 100. Specifically, a first capacitor 302 is electricallyconnected between the upper excitation electrode 21 of the crystaloscillator 100 and ground, and a second capacitor 304 is electricallyconnected between the lower excitation electrode 22 of the crystaloscillator 100 and ground. The matching capacitor 300 is provided foradjustment (matching adjustment) so that the output frequency (initialvalue) of the crystal oscillator 100 becomes a desired value (designedvalue) when the total capacitance (load capacitance value) in theoverall circuit of the IC 200 including the crystal oscillator 100 isadded. It is noted that, in FIG. 4, an area surrounded by a dotted lineforms an oscillation circuit.

The IC 200 includes an inverting amplifier 206, an output buffer (buffercircuit) 208, an alarm issuing circuit 250 (an example of an alarmgenerator), a gain control circuit 260 (an example of a gain controlunit), and a reference voltage generating unit 270.

As described above, the inverting amplifier 206 inverts and amplifiesthe output of the crystal oscillator 100 (the signal input from theupper excitation electrode 21 to the input terminal 202). That is, thesignal input from the upper excitation electrode 21 to the inputterminal 202 is inverted and amplified by the inverting amplifier 206.The inverted and amplified signal is input to the output buffer 208 andinput to the lower excitation electrode 22 via the output terminal 204.

The gain (gain) of the inverting amplifier 206 is variable. It is notedthat the inverting amplifier 206 may be of a type that is used for AGC(Automatic Gain Control) (for example, a type that uses a variableresistor or a field effect transistor as a variable resistance element).However, in the first embodiment, control for adjusting the gain of theinverting amplifier 206 (i.e., the automatic gain control) to alwayskeep the output constant is not performed, as described hereinafter.That is, no automatic gain control circuit is provided. As a result,since a circuit configuration for automatic gain control becomesunnecessary, a simple configuration can be realized, and power savingcan be achieved.

In the first embodiment, as an example, as illustrated in FIG. 5, theinverting amplifier 206 includes an operational amplifier OP, a resistorR2 (an example of a first resistor), and a resistor R3 (an example of asecond resistor). The resistors R2 and R3 are provided in parallel on aline which is provided for returning the output of the operationalamplifier OP to the inverting terminal. The inverting amplifier 206further includes a switch SW. The switch SW has a first state in whichan inverting terminal of the operational amplifier OP is electricallyconnected to an output terminal of the operational amplifier OP via theresistor R2, and a second state in which the inverting terminal of theoperational amplifier OP is electrically connected to the outputterminal of the operational amplifier OP via the resistor R3. The stateof the switch SW is controlled by the gain control circuit 260. In thefirst state, the relationship between the input voltage Vi and theoutput voltage Vo is Vo=R2/R1×Vi, and R2/R1 is the amplification factor.In the second state, the relationship between the input voltage Vi andthe output voltage Vo is Vo=R3/R1×Vi, and R3/R1 is the amplificationfactor. For example, if R3>R2, since R3/R1>R2/R1, the amplificationfactor (that is, the gain of the inverting amplifier 206) becomes higherin the second state than in the first state. According to the exampleillustrated in FIG. 5, it is possible to realize the inverting amplifier206 whose gain is variable with a simple configuration, as compared withthe inverting amplifier of the type using a variable resistor or thelike.

The output buffer 208 may be formed by a CMOS (Complementary Metal OxideSemiconductor), for example. The output buffer 208 generates a signal(pulse signal) representing the oscillation state of the crystaloscillator 100 based on the input signal (the signal inverted andamplified by the inverting amplifier 206). The output buffer 208 outputs“voltage VOH” when the level of the input signal (hereinafter alsoreferred to as “input level”) exceeds a first threshold value andoutputs “voltage VOL” when the input level becomes lower than a secondthreshold value. It is noted that the first threshold value and thesecond threshold value may be set to the same or may be set differently,depending on a voltage value (threshold level) at which a P-type MOS anda N-type MOS, which form the CMOS of the output buffer 208, are turnedon/off. In this way, in the example illustrated in FIG. 4, the output ofthe crystal oscillator 100 is not directly output from the crystaloscillator 100 but is output to the clock output terminal 220 via theoutput buffer 208.

The alarm issuing circuit 250 has a function (hereinafter referred to as“pre-output stop state detection function”) for detecting a state(hereinafter referred to as “pre-output stop state”) before the crystaloscillator 100 stops outputting. It is noted that, the fact that thecrystal oscillator 100 stops outputting means that the oscillationcircuit stops outputting. The fact that the crystal oscillator 100 stopsoutputting means the transition to the state in which the output fromthe output buffer 208 does not change (i.e., the state in which a normaloutput, which alters between “VOH” and “VOL” at the cycle correspondingto the output frequency of the crystal oscillator 100, cannot beobtained.

The alarm issuing circuit 250 is electrically connected to the coil 50.The alarm issuing circuit 250 realizes the pre-output stop statedetection function by monitoring the signal appearing in the coil 50.The alarm issuing circuit 250 generates an alarm when the amplitude ofthe signal appearing in the coil 50 (the amplitude of the voltagewaveform generated across the coil 50) becomes equal to or less than apredetermined reference value R. The amplitude of the signal may bebased on the difference between the maximum value and the average valueof the level of the signal for the most recent predetermined period, thedifference between the average value and the minimum value of the levelof the signal for the latest predetermined period, half of thedifference between the maximum value and the minimum value of the levelof the signal for the latest predetermined period, etc. It is noted thatthe alarm issuing circuit 250 may use the maximum value of the level ofthe signal for the latest predetermined period as the amplitude. This isbecause, for example, the maximum value of the signal level of the mostrecent one cycle is correlated with the amplitude of the same signal inthe same cycle. Alternatively, the alarm issuing circuit 250 may useintegrated value of the amplitude values of the signal over the latestpredetermined period as the amplitude.

The reference value β is set to a value greater than the amplitude Am ofthe signal appearing in the coil 50 when the amplitude of the input tothe output buffer 208 becomes an input lower limit value. For example,the reference value β may be β=1.1×Am or β>1.1×Am. The input lower limitvalue of the output buffer 208 corresponds to the lower limit value ofthe input level (magnitude of the input voltage) to the output buffer208 when the output is obtained from the output buffer 208. That is,even if the input to the output buffer 208 alters periodically, asignificant output from the output buffer 208 (an output that canfunction as a clock source) cannot be obtained in a state in which thelevel of the input to the output buffer 208 is below a certain lowerlimit value and thus the CMOS is not turned on/off. The input lowerlimit value of the output buffer 208 corresponds to the lower limitvalue. It is noted that the reference value β may be uniformly set basedon a design value of the input lower limit value of the output buffer208. Alternatively, the reference value β may be set for each individualbased on measured values for individuals, corresponding to input lowerlimit values or the like which may differ for each individual of theoutput buffer 208. In this case, for example, the reference value β maybe set based on an actually measured value at the time of shipment of aproduct including the crystal oscillator 100 and the IC 200 (forexample, an actually measured value of the amplitude Am).

The alarm generated by the alarm issuing circuit 250 is output to theoutside via the alarm output terminal 222 and input to the gain controlcircuit 260. It is noted that the alarm output via the alarm outputterminal 222 may be transmitted to, for example, an external user device(not illustrated). When the output of the crystal oscillator 100functions as a clock of the communication control device, the userdevice may be, for example, a central management server that manages abase station or the like. In this case, the alarm may be a signalcausing an alarm output including a voice or a display, or may includeinformation of an index value (for example, the current value of theamplitude of the signal appearing in the coil 50) representing thelowered state of the current oscillation level. Upon receipt of such analarm output, for example, a user who is a telecommunications carrier,can plan the repair/replacement work for the communication controldevice that includes the crystal oscillator 100 (the crystal oscillator100 in which the pre-output stop state was detected).

The gain control circuit 260 has a function of increasing the gain ofthe inverting amplifier 206 in synchronization with the occurrence ofthe alarm. That is, when an alarm from the alarm issuing circuit 250 isinput, the gain control circuit 260 increases the gain of the invertingamplifier 206 from a first value to a second value. The second value issignificantly greater than the first value, for example the maximumvalue of the variable range. This increases the amplitude of the outputfrom the inverting amplifier 206 and increases the amplitude of theinput to the output buffer 208. In the example illustrated in FIG. 5,when the alarm from the alarm issuing circuit 250 is input, the gaincontrol circuit 260 controls the switch SW to switch from the firststate to the second state (see the arrow in FIG. 5). As a result, thegain of the inverting amplifier 206 increases from R2/R1 to R3/R1.

The gain control circuit 260 maintains the gain of the invertingamplifier 206 at the first value until the alarm from the alarm issuingcircuit 250 is input, and when the alarm is input, the gain of theinverting amplifier 206 is set to the second value, and thereafter, thegain of the inverting amplifier 206 is maintained at the second value.In this case, the first value (R2/R1) is smaller than the second value(R3/R1). Accordingly, while power saving is implemented until the alarmfrom the alarm issuing circuit 250 is input, the state in which the gainof the inverting amplifier 206 is increased can be maintained after thealarm from the alarm issuing circuit 250 is input.

The reference voltage generating unit 270 generates a voltagecorresponding to the reference value β used in the alarm issuing circuit250. For example, the voltage generated by the reference voltagegenerating unit 270 may be input to a comparator (not illustrated) ofthe alarm issuing circuit 250.

Next, with reference to FIGS. 6 to 8D, effects of the first embodimentare described. Hereinafter, in some cases, the effects of the firstembodiment will be described in comparison with a comparative examplewhich does not include the gain control circuit 260.

FIG. 6 is an explanatory diagram of characteristics in a case where thecrystal oscillator 100 is a normal product.

FIG. 6 illustrates, on the upper side, a frequency characteristicdiagram illustrating the time-varying characteristics of the outputfrequency of the crystal oscillator 100, taking the time on thehorizontal axis and the output frequency of the crystal oscillator 100on the vertical axis. In the frequency characteristic diagram, afrequency standard lower limit value with respect to the outputfrequency of the crystal oscillator 100 is illustrated, and the timevariation characteristic F1 related to a normal product is illustrated.

FIG. 6 illustrates, on the lower side, an output change characteristicdiagram indicating the time-varying characteristics C1 a, C1 b, C1 c ofthe amplitudes at each point A, B, C, respectively, taking the time onthe horizontal axis and the amplitude of the signal appearing at eachpoint A, B, C in the oscillation circuit illustrated in FIG. 4 on thevertical axis. In the output change characteristic diagram, the inputlower limit value of the output buffer 208 is also illustrated.

In the case of a normal product, the output frequency of the crystaloscillator 100 decreases from the value f0 in a proportional manner withrespect to the exponential increase in time, as illustrated by the timevariation characteristic F1 on the upper side of FIG. 6 due to aging(aged deterioration). However, in the case of a normal product, theoutput frequency of the crystal oscillator 100 does not fall below thefrequency standard lower limit value before the design life (forexample, 6 years). It is noted that the main cause of the frequencychange is the oxidation of the excitation electrodes 20 of the crystaloscillator 100. The amount of the frequency change due to aging can becontrolled to some extent by management of the manufacturing process orthe like. If the crystal oscillator 100 is as designed, the outputfrequency of the crystal oscillator 100 does not fall below thefrequency standard lower limit value before the design life, asillustrated in FIG. 6.

In the case of a normal product, the amplitude of the signal appearingat the point B in the oscillation circuit illustrated in FIG. 4decreases due to aging as indicated by the time variation characteristicC1 b on the lower side of FIG. 6. As in the case of the frequencychange, the main cause of the amplitude change is the mass increase dueto the oxidation of the excitation electrode 20 of the crystaloscillator 100. However, in the case of a normal product, before thedesign life, the amplitude of the signal appearing at the point Billustrated in FIG. 4 does not fall below the input lower limit value ofthe output buffer 208. That is, if the crystal oscillator device isconfigured as designed, the amplitude of the input to the output buffer208 does not fall below the input lower limit value before the designlife. Therefore, in the case of a normal product, the amplitude of thesignal appearing at the point C illustrated in FIG. 4 does not changeand is constant as indicated by the time variation characteristic C1 con the lower side of FIG. 6. That is, in the case of a normal product,until the design life, the output (that is, normal output) switchingbetween “VOH” and “VOL” at the cycle corresponding to the outputfrequency of the crystal oscillator 100 can be obtained at the point Cillustrated in FIG. 4.

FIGS. 7 to 8D are explanatory diagrams of output stoppage of the crystaloscillator 100 caused by abnormality. In FIG. 7, t1 represents a timepoint at which the crystal oscillator 100 starts to operate, t2represents a time point immediately before the crystal oscillator 100stops outputting, t3 represents a time point when the crystal oscillator100 stops outputting, and t4 represents the point of design life.

FIG. 7 illustrates, on the upper side, a frequency characteristicdiagram illustrating the time-varying characteristics of the outputfrequency of the crystal oscillator 100, taking the time on thehorizontal axis and the output frequency of the crystal oscillator 100on the vertical axis. In the frequency characteristic diagram, thefrequency standard lower limit value with respect to the outputfrequency of the crystal oscillator 100 is illustrated, and the timevariation characteristic F1 (dotted line) related to a normal productand the time variation characteristic F2 (solid line) related to anabnormal product that stops outputting before the design life areillustrated. As an example, the time variation characteristic F2relating to an abnormal product indicates a case where the output stopsafter about 100 days from the start of operation.

FIG. 7 illustrates, on the lower side, an output change characteristicdiagram indicating the time-varying characteristics C2 a, C2 b, C2 c(i.e., the time-varying characteristics related to an abnormal product)of the amplitudes at each point A, B, C, respectively, taking the timeon the horizontal axis and the amplitude of the signal appearing at eachpoint A, B, C in the oscillation circuit illustrated in FIG. 4 on thevertical axis. In the output change characteristic diagram, the inputlower limit value of the output buffer 208, and the time variationcharacteristic C1 c (dotted line) related to a normal product are alsoillustrated.

FIGS. 8A to 8D are diagrams illustrating time-series waveforms of thesignal appearing in the case of an abnormal product. FIG. 8A illustratesthe waveform of the signal appearing at point A illustrated in FIG. 4.FIG. 8B illustrates the waveform of the signal appearing at point Billustrated in FIG. 4. FIG. 8C illustrates the waveform of the signalappearing at point C illustrated in FIG. 4. FIG. 8D illustrates thewaveform of the signal appearing in the coil 50. In FIG. 8A to FIG. 8D,from the top, the waveform within a certain time period from the timepoint t1, the waveform within a certain time period before time pointt2, and the waveform within a certain time period from time point t3 areillustrated. In FIG. 8B, a positive voltage value Vmin having the samemagnitude as the input lower limit value and a negative voltage valueVmin having the same magnitude as the input lower limit value are alsoillustrated. In addition, in FIG. 8C, the voltage level “High” to beexceeded in a positive direction by the output VOH and the voltage level“Low” to be exceeded in a negative direction by the output VOL are alsoillustrated. In addition, the reference value β is also illustrated inFIG. 8D.

Here, there are cases where the decrease rate of the output frequency ofthe crystal oscillator 100 and the oscillation level become significantdue to abnormality of a manufacturing process or contamination fromcontaminants. In such a case, an abnormal product that causes outputstoppage before the design life may be generated.

Specifically, in the case of an abnormal product, the output frequencyof the crystal oscillator 100 decreases from the initial value f0 withdecrease speed significantly higher than the decrease speed due to agingin a normal product, as illustrated in the time variation characteristicF2 on the upper side of FIG. 7. In the case where the output of thecrystal oscillator 100 is used as the clock of the standalone system,even if the frequency decrease progresses up to the time t2, there is apossibility that the frequency decrease may be permissible with a slightdecrease in calculation speed. However, at time t3, the output suddenlystops and the whole system goes down.

More specifically, in the case of an abnormal product, the amplitude ofthe signal appearing at the point A in the oscillation circuitillustrated in FIG. 4 decreases by a significantly greater amount thanthe decrease amount due to aging in the case of a normal product, asillustrated in the time variation characteristic C2 a on the lower sidein FIG. 7 and FIG. 8A. Correspondingly, in the case of an abnormalproduct, the amplitude of the signal appearing at the point B in theoscillation circuit illustrated in FIG. 4 decreases by a significantlygreater amount than the decrease amount due to aging in the case of anormal product, as illustrated in the time variation characteristic C2 bon the lower side in FIG. 7 and FIG. 8B. Thus, in the case of anabnormal product, before the design life, the amplitude of the signalappearing at the point B illustrated in FIG. 4 may fall below the inputlower limit value of the output buffer 208.

In this respect, in the case of an abnormal product illustrated in FIG.7, in the comparative example, the amplitude of the signal appearing atthe point B in the oscillation circuit illustrated in FIG. 4 falls belowthe input lower limit value of the output buffer 208 at the time t3, asillustrated in the time variation characteristic C2 b on the lower sideof FIG. 7 and FIG. 8B. In this way, in the case of an abnormal productillustrated in FIG. 7, the amplitude of the signal appearing at thepoint B in the oscillation circuit illustrated in FIG. 4, that is, theamplitude of the input to the output buffer 208 falls below the inputlower limit value before the design life. If the amplitude of the inputto the output buffer 208 falls below the input lower limit value of theoutput buffer 208, the signal level appearing at the point C illustratedin FIG. 4 becomes a constant value 0, as illustrated in the timevariation characteristic C2 c on the lower side of FIG. 7 and FIG. 8C.That is, prior to the design life, the crystal oscillator 100 stopsoutputting while the crystal oscillator 100 remains in the oscillationstate (see FIG. 8A).

Here, the abnormality of the crystal oscillator 100 often causesabnormal frequency change. Since the oscillation circuit including thecrystal oscillator 100 itself is a clock generation source, a referenceclock with higher accuracy may be required to directly detect thefrequency change of the crystal oscillator 100. Therefore, it isdifficult to detect the abnormality in the frequency of the crystaloscillator 100 (for example, a characteristic like the time variationcharacteristic F2 in FIG. 7) by a simple method.

In this respect, the frequency change of the crystal oscillator 100 dueto contamination from contaminants or the like correlates with thechange (decrease) in the oscillation level of the crystal oscillator 100as illustrated in FIGS. 6 and 7. This is because, in the case where themass of the excitation electrodes 20 is increased due to contaminationfrom contaminants, for example, both the output frequency and theoscillation level of the crystal oscillator 100 are reduced due to themass increase. Therefore, even when the frequency change of the crystaloscillator 100 cannot be directly detected, it may be possible toindirectly detect the frequency change of the crystal oscillator 100 bymonitoring the oscillation level of the crystal oscillator 100.

On the other hand, as described above, the output of the crystaloscillator 100 is not directly output from the oscillation circuitincluding the crystal oscillator 100 but output through the outputbuffer 208. As illustrated in FIG. 7, etc., as long as the amplitude ofthe input exceeds the input lower limit value of the output buffer 208,the output of the output buffer 208 oscillates between the output VOHand the output VOL at the frequency that corresponds to the outputfrequency, even in the case of an abnormal product. The levels of theoutput VOH and the output VOL are substantially constant as long as theamplitude of the input exceeds the input lower limit value of the outputbuffer 208 even in the case of an abnormal product. Therefore, based onthe output from the output buffer 208, it is not possible to directlyread the abnormality of the oscillation circuit (for example, theabnormality of the crystal oscillator 100). Therefore, the failure ofthe oscillation circuit including the crystal oscillator 100 is oftenrecognized only when its output falls below the standard (for example,the frequency standard lower limit value) or when the output stops. Itis noted that there may be often the case that the main cause of failureof the oscillation circuit resulted from the crystal oscillator 100included therein.

As described above, the abnormality of the crystal oscillator 100 isoften known only after the crystal oscillator 100 has stoppedoutputting. This means that the repair/replacement timing of the crystaloscillator 100 suddenly comes in, which is significantly inconvenientfor a user of a system using an output from the oscillation circuitincluding the crystal oscillator 100 as a clock source. Especially, whenthe crystal oscillator 100 is used in a system that requires highreliability, the adverse effect when the system suddenly goes down maybe significant. In addition, when the crystal oscillator 100 is used ina relay station device or the like installed in a remote mountainousarea or the like, it may take time to repair or exchange it, which mayincrease the down time of the system. Although such a disadvantage canbe avoided to some extent by providing a redundant system, providing aredundant system adds cost.

In this regard, according to the first embodiment, as described above,the alarm issuing circuit 250 generates the alarm when the amplitude ofthe signal appearing in the coil 50 becomes equal to or less than thereference value β. As described above, the reference value β is set to avalue greater than the amplitude Am of the signal when the amplitude ofthe input to the output buffer 208 becomes the input lower limit value.Therefore, according to the first embodiment, the alarm can be generatedby the alarm issuing circuit 250 before the amplitude of the signalappearing at the point B in the oscillation circuit illustrated in FIG.4 falls below the input lower limit value of the output buffer 208. As aresult, it is possible to notify the user of the system using the outputfrom the oscillation circuit including the crystal oscillator 100 as theclock source in advance the necessity of repair/replacement due to thealarm. That is, before the crystal oscillator 100 stops outputting, theuser can be notified of necessity of repair/replacement by the alarm inadvance. As a result, it is possible to avoid situations where thesystem suddenly goes down if the user, who is notified of necessity ofrepair/replacement by the alarm in advance, plans appropriaterepair/replacement work.

In addition, according to the first embodiment, as described above, thegain control circuit 260 increases the gain of the inverting amplifier206 in synchronization with the occurrence of the alarm. When the gainof the inverting amplifier 206 is increased, the amplitude of the outputfrom the inverting amplifier 206 (the amplitude of the input to theoutput buffer 208) increases. Therefore, according to the firstembodiment, the amplitude of the input to the output buffer 208 can beincreased in synchronization with the occurrence of the alarm, and as aresult, the period until the crystal oscillator 100 stops outputting canbe extended. That is, according to the first embodiment, even in thecase of an abnormal product, the period until the crystal oscillator 100stops outputting can be extended in response to the occurrence of thealarm. As a result, it becomes easier for the user to secure thenecessary time for executing appropriate repair/replacement work. Thiseffect is particularly useful when the crystal oscillator 100 is usedfor a relay station apparatus or the like installed in a remotemountainous area or the like. This is because, in such a case, it takestime for repair and exchange work in many cases.

Further, in the above-described first embodiment, since the output ofthe crystal oscillator 100 in the oscillating state can be monitored viathe coil 50 and the magnet 59, a monitoring system independent of theoscillation circuit can be formed. Therefore, according to the firstembodiment, it is possible to monitor the output of the crystaloscillator 100 in the oscillating state in a manner that does not affectthe oscillation circuit.

FIG. 9 is a diagram explaining an example of an operation according tothe first embodiment. In FIG. 9, t1 represents a time point at which thecrystal oscillator 100 starts to operate, t5 represents a detection timeof the pre-output stop state, t6 represents a time point when thecrystal oscillator 100 stops outputting, and t4 represents the point ofdesign life. Further, in FIG. 9, the output stop time t3 in the case ofFIG. 7 is illustrated for comparison. FIG. 9 illustrates a case wherethe crystal oscillator 100 is not repaired or replaced until the crystaloscillator 100 stops outputting.

FIG. 9 illustrates, as in the case of FIG. 7 described above, on theupper side, a frequency characteristic diagram illustrating thetime-varying characteristics of the output frequency of the crystaloscillator 100, taking the time on the horizontal axis and the outputfrequency of the crystal oscillator 100 on the vertical axis. In thefrequency characteristic diagram, the frequency standard lower limitvalue with respect to the output frequency of the crystal oscillator 100is illustrated, and the time variation characteristic F1 (dotted line)related to a normal product and the time variation characteristic F3(solid line) related to an abnormal product that stops outputting beforethe design life are illustrated. The abnormal product in FIG. 9 isassumed to be the same as the abnormal product in FIG. 7.

FIG. 9 illustrates, similar to FIG. 7, on the lower side, an outputchange characteristic diagram indicating the time-varyingcharacteristics C3 a, C3 b, C3 c, C3 d (i.e., the time-varyingcharacteristics related to an abnormal product), taking the time on thehorizontal axis and the amplitude. Time-varying characteristics C3 d isthe time-varying characteristics of the amplitude of the signalappearing in the coil 50 (the same characteristics according to anabnormal product). In the output change characteristic diagram, theinput lower limit value of the output buffer 208, the reference value β,and the time variation characteristic C1 c (dotted line) related to anormal product are also illustrated.

In the case of an abnormal product, similar to FIG. 7, the outputfrequency of the crystal oscillator 100 is significantly higher than thedecrease speed due to aging in a normal product, as illustrated in thetime variation characteristic F3 on the upper side of FIG. 9. However,in the first embodiment, as described above, unlike FIG. 7, the gaincontrol circuit 260 functions to prevent the entire system from stoppingoutputting and thus being down at time t3. That is, even in the case ofan abnormal product, as illustrated in the time varying characteristicF3 at the top of FIG. 9, until time t6 after time t3, it is possible todelay the timing at which the entire system is down. It is noted that,in the example illustrated in FIG. 9, a timing when the output frequencyof the crystal oscillator 100 falls below the frequency standard lowerlimit value is the same as a timing when the entire system is down(i.e., the timing at which the level of the signal appearing at point Cbecomes the constant value 0); however, this is not indispensable.However, preferably, the timing, at which the output frequency of thecrystal oscillator 100 falls below the frequency standard lower limitvalue, does not arrive before the timing at which the entire system isdown.

Further, in the case of an abnormal product, the amplitude of the signalappearing at the point A in the oscillation circuit illustrated in FIG.4 decreases by a significantly greater amount than the decrease due toaging in the case of a normal product, as illustrated in the timevariation characteristic C3 a on the lower side in FIG. 9. Thus, in thecase of an abnormal product, the amplitude of the signal appearing atthe point B in the oscillation circuit illustrated in FIG. 4 decreasesby a significantly greater amount than the decrease due to aging in thecase of a normal product, as illustrated in the time variationcharacteristic C3 b on the lower side in FIG. 9. Thus, in the case of anabnormal product, similar to FIG. 7, before the design life, theamplitude of the signal appearing at the point B illustrated in FIG. 4may fall below the input lower limit value of the output buffer 208.

In this regard, according to the first embodiment, as schematicallyillustrated by an arrow at the bottom of FIG. 9, the alarm is generatedat time t5 at which the amplitude of the signal appearing in the coil 50is equal to or less than a reference value β. Accordingly, the gain ofthe inverting amplifier 206 is increased, and, as illustrated in thetime varying characteristic C3 b at the lower side of FIG. 9, theamplitude (i.e., the amplitude of the input to the output buffer 208) ofthe signal appearing at point B in the oscillation circuit illustratedin FIG. 4 increases. It is noted that, accordingly, the oscillationlevel of the crystal oscillator 100 is increased, the amplitude of thesignal appearing at point A in the oscillation circuit illustrated inFIG. 4 increases, as illustrated in the time varying characteristic C3 aat the lower side of FIG. 9. Thus, at time t5, the amplitude of thesignal appearing at point B in the oscillation circuit illustrated inFIG. 4 increases. However, because of an abnormal product, even at timet5, the amplitude of the signal appearing at point B in the oscillationcircuit illustrated in FIG. 4 continues to decrease by the decreaseamount significantly greater than the decrease amount due to the agingof a normal product. Then, before the design life, the amplitude of thesignal appearing at the point B illustrated in FIG. 4 may fall below theinput lower limit value of the output buffer 208. In the case of anabnormal product illustrated in FIG. 9, the amplitude of the signalappearing at the point B in the oscillation circuit illustrated in FIG.4 falls below the input lower limit value of the output buffer 208 atthe time t6, as illustrated in the time variation characteristic C3 b onthe lower side of FIG. 9. In this way, in the case of an abnormalproduct illustrated in FIG. 9, the amplitude of the signal appearing atthe point B in the oscillation circuit illustrated in FIG. 4, that is,the amplitude of the input to the output buffer 208 falls below theinput lower limit value before the design life, and thus the crystaloscillator 100 transitions to the output stop state. However, in thefirst embodiment, as can be seen in comparison with FIG. 7, a timing t6when the crystal oscillator 100 transitions to the output stop state,comes later than the timing t3 in FIG. 7. That is, in the firstembodiment, even in the case of an abnormal product, as compared withthe comparative example, the timing when the crystal oscillator 100transitions to the output stop state can be delayed. In other words, inthe first embodiment, as compared with the comparative example, therepair or replacement timing of the crystal oscillator 100 can bedelayed by a period of time t3 to time t6. It is noted that, in theexample illustrated in FIG. 9, if the repair or replacement of thecrystal oscillator 100 is performed during the period from time t3 totime t6, it is possible to avoid a situation where the system ends updown suddenly at time t6.

It is noted that, in the first embodiment described above, the functionsof the alarm issuing circuit 250, the gain control circuit 260, and thereference voltage generating unit 270 are implemented by the IC 200;however, at least a part of the functions may be realized by a computer.For example, the functions of the alarm issuing circuit 250 and the gaincontrol circuit 260 may be implemented by a CPU of the computerexecuting a program, and the function of the reference voltagegenerating unit 270 may be implemented by a memory of the computer.

FIGS. 10A and 10B are explanatory views of another exampleimplementation of a magnet 59, a crystal oscillator 100A, and areschematic cross-sectional views of crystal oscillators 100A and 100B. Itis noted that FIGS. 10A and 10B correspond to a cross-sectional viewtaken along a line B-B in FIG. 1A. In FIGS. 10A and 10B, a polarity (Npole, S pole) of the magnet 59 is schematically illustrated as “N” and“S”. It is noted that FIGS. 10A and 10B illustrate the IC 200 inaddition to the crystal oscillators 100A and 100B.

According to the crystal oscillator 100A illustrated in FIG. 10A, amagnet 59 is provided such that the magnet 59 forms a part of the casing30. The magnet 59, as illustrated in FIG. 10A, may be embedded in thecasing 30. However, the magnet 59 may be also formed by applying amagnetic flux generating material on the casing 30. It is noted thateither of the N pole and the S pole in the magnet 59 may be on the upperside.

In the crystal oscillator 100B illustrated in FIG. 10B, the magnet 59 isprovided such that the magnet 59 is parallel to the surface of thecrystal piece 10 and does not contact the crystal piece 10. In thiscase, the magnet 59 may be in a form of a substrate, or may be formed byapplying a magnetic flux generating material to a substrate. Further,the magnet 59 may be supported by the crystal piece 10 or the casing 30by suitable support means (not illustrated). It is noted that either ofthe N pole and the S pole in the magnet 59 may be on the upper side.

In the example illustrated in FIGS. 10A and 10B, the magnet 59 isprovided on the casing 30 or in the casing 30; however, the magnet 59may be provided outside the casing 30.

FIG. 10C is a diagram explaining another example of implementation of amagnetic flux generating member other than a magnet. According to acrystal oscillator 100C illustrated in FIG. 10C, an electromagnet 57instead of the magnet 59 is used. The electromagnet 57 may be providedat a position where the density of the magnetic flux passing through thecoil 50 is maximum in the neutral state (for example, in a state of notoscillating) of the crystal piece 10. The electromagnet 57, asillustrated schematically in FIG. 10C, may be provided outside thecasing 30, or may be provided in the casing 30.

Second Embodiment

A crystal oscillator device according to the second embodiment differsfrom the crystal oscillator device according to the first embodimentdescribed above in that the crystal oscillator 100 is replaced with acrystal oscillator 100D. The crystal oscillator 100D according to thesecond embodiment differs from the crystal oscillator 100 according tothe first embodiment described above in that the coil 50 is replacedwith a coil 50D. Other elements of the crystal oscillator 100D accordingto the second embodiment may be the same as those of the crystaloscillator 100 according to the first embodiment described above, andexplanation thereof is omitted.

FIG. 11 is a diagram explaining an example of implementation of a coil50D according to the second embodiment, and a two-side view (plan viewsillustrating an upper surface and a lower surface) of a crystal piece10. FIG. 12 is a diagram illustrating a cross-sectional view along aline D-D in FIG. 11. FIG. 13 is a schematic cross-sectional view of thecrystal oscillator 100D. It is noted that FIG. 13 corresponds to across-sectional view along a line B-B in FIG. 1A. In FIG. 13, a polarity(N pole, S pole) of a magnet 59 is schematically illustrated as “N” and“S”. Further, in FIG. 13, in addition to the crystal oscillator 100D,the IC 200D is also illustrated.

The coil 50D differs from the coil 50 according to the first embodimentdescribed above in that coil pattern portions 511D and 521D areelectrically connected, without substantially using the through hole 56.

Specifically, the coil 50D includes the coil pattern portions 511D and521D, and the wiring portion 512 and 522, wiring portion 541D and 542D,and a midpoint electrode 58D. The ends (the center side of the turns) ofthe coil pattern portions 511D and 521D are electrically connected tothe wiring portion 541D and 542D, respectively. The wiring portions541D, 542D extend in the X direction towards the free end of the crystalpiece 10 in the X direction (the end on the side farther from the bankportion 31) to be electrically connected to the midpoint electrode 58D.The crystal piece 10 includes insulating films 71 and 72 (an example ofinsulating portions) formed on the coil pattern portion 511 and 521.That is, parts of the coil pattern portions 511 and 521 are covered withthe insulating films 71 and 72. The wiring portions 541D, 542D areformed on the insulating films 71 and 72, and thus are electricallyinsulated from the portion of the coil pattern portion 511 and 521located below (see FIG. 12), respectively. The midpoint electrode 58D isformed on the upper surface and the lower surface of the crystal piece10 via the side surface of the crystal piece 10 (i.e., the side surfaceon the free end side of the crystal piece 10). In this way, the ends(center side of the turns) of the coil pattern portion 511 and 521 areelectrically connected via the wiring portions 541D, 542D and themidpoint electrode 58D. The midpoint electrode 58D may extend betweenthe upper surface and the lower surface via a through hole. The otherends of the coil pattern portions 511 and 521 are electrically connectedto the electrode 52 and the electrode 54 via the wiring portions 512 and522, respectively, similarly to the coil 50 according to firstembodiment described above.

In the examples illustrated in FIGS. 11 and 13, the coil 50D is formedon both the upper surface and the lower surface of the crystal piece 10in order to increase the number of turns; however, the coil 50D may beformed on only one of the upper surface and the lower surface of thecrystal piece 10. Further, in the examples illustrated in FIGS. 11 and13, the coil pattern portions 511 and 521 are formed in a plurality ofturns in order to increase the number of windings, but may be woundonce. Further, in the examples illustrated in FIGS. 11 and 13, the coilpattern portions 511 and 521 are provided on the farther side from thebank portion 31 in the X direction with respect to the excitationelectrodes 20 (i.e., the free end side of the crystal piece 10);however, the coil pattern portions 511 and 521 may be provided at anarbitrary position with respect to the excitation electrodes 20. Forexample, the coil pattern portions 511 and 521 may be provided on theside closer to the bank portion 31 in the X direction with respect tothe excitation electrodes 20.

Also, according to the second embodiment, the same effects as in thefirst embodiment can be obtained. It is noted that, in the secondembodiment, it is possible to implement the modifications as describedabove and illustrated in FIGS. 10A to 10C. That is, in the secondembodiment, the magnet 59 may be provided such that the magnet 59 formsa part of the casing 30 (see FIG. 10A), may be provided in a form of asubstrate (see FIG. 10B), or may be replaced with an electromagnet (seeFIG. 10C).

Third Embodiment

A crystal oscillator device according to the third embodiment differsfrom the crystal oscillator device according to the first embodimentdescribed above in that the crystal oscillator 100 is replaced with acrystal oscillator 100E. The crystal oscillator 100E according to thethird embodiment differs from the crystal oscillator 100 according tothe first embodiment described above in that the crystal piece 10, thecoil 50, and the magnet 59 are replaced with a crystal piece 10E, a coil50E, and a magnet 59E, respectively. Further, the crystal oscillator100E according to the third embodiment differs from the crystaloscillator 100 according to the first embodiment described above in thatthe lid 34 of the casing 30 is replaced with a lid 34E. Other elementsof the crystal oscillator 100E according to the second embodiment may bethe same as those of the crystal oscillator 100 according to the firstembodiment described above, and explanation thereof is omitted.

FIG. 14 is a diagram explaining an example of implementation of a coil50E according to the third embodiment, and a two-side view (plan viewsillustrating an upper surface and a lower surface) of a crystal piece10E. FIG. 15 is a diagram illustrating a cross-sectional view along aline E-E in FIG. 14. FIG. 16 is a diagram explaining an example ofimplementation of the magnet 59E, and is a schematic cross-sectionalview of the crystal oscillator 100E. It is noted that FIG. 16corresponds to a cross-sectional view along a line B-B in FIG. 1A. InFIG. 16 (in FIGS. 17A and 17B, as well), the polarity of the magnet 59E(N pole) is schematically indicated by “N”. Further, in FIG. 16, inaddition to the crystal oscillator 100E, the IC 200 is also illustrated.

The crystal piece 10E differs from the crystal piece 10 according to thefirst embodiment described above in that a slit 12E penetrating in thethickness direction of the crystal piece 10E is formed. The slit 12E,for example, as illustrated in FIG. 14, may be provided on the fartherside (free end side of the crystal piece 10E) from the bank portion 31in the X direction with respect to the excitation electrodes 20.Hereinafter, a portion of the crystal piece 10E, which closer to thefree end side of the crystal piece 10E with respect to the slit 12E inthe X direction, is referred to as “coil forming portion 13E”. The coilforming portion 13E extends along the longitudinal direction (Ydirection) of the slit 12E, as illustrated in FIG. 14.

The coil 50E differs from the coil 50 according to the first embodimentdescribed above in that coil pattern part 511E and 521E are electricallyconnected, without substantially using the through hole 56.

Specifically, the coil 50E includes the coil pattern portions 511E,521E, wiring sections 512, 522E, and connecting portions 551E, 552E. Thecoil pattern portions 511E and 521E are electrically connected via theconnecting portions 551E and 552E, respectively. The coil patternportions 511E, 521E, and the connecting portions 551E, 552E form aspiral-shaped coil pattern in cooperation, when viewed in the Ydirection. In other words, the coil pattern portions 511E, 521E, and theconnecting portions 551E, 552E form a coil pattern as a whole which iswound around the coil forming portion 13E. More specifically, the coilpattern portion 511E is formed on the upper surface of the crystal piece10E. The coil pattern portion 511E extends obliquely in a plan view(direction perpendicular to the surface of the crystal piece 10E), andincludes a plurality of conductor patterns offset from each other in theY direction. The coil pattern portion 521E is formed on the lowersurface of the crystal piece 10E. The coil pattern portion 521E extendsobliquely in a plan view (direction perpendicular to the surface of thecrystal piece 10E), and includes a plurality of conductor patternsoffset from each other in the Y direction. The ends (i.e., the ends onthe free end side of the crystal piece 10E) of the conductor patterns ofcoil pattern portion 511E and coil pattern portion 521E are electricallyconnected via the connecting portion 552E that is formed on the sidesurface of the free end side of the crystal piece 10E. The other ends ofthe conductor patterns of the coil pattern portion 511E and the coilpattern portion 521E are electrically connected via the connectingportion 551E that is formed on the side surface of the slit 12E.Hereinafter, a portion in form of a spiral coil pattern in the coil 50Eis referred to as “spiral pattern portion of the coil 50E”. The end ofthe spiral pattern portion of the coil 50E is electrically connected tothe electrode 52 via the wiring portion 512, as illustrated in FIG. 14.Further, the other end of the spiral pattern portion of the coil 50E iselectrically connected to the electrodes 54E through the wiring portion522E. The wiring portions 522E and electrode 54E may be formed on theupper surface of the crystal piece 10E, as illustrated in FIG. 14.However, the wiring portion 522E and electrode 54E may be formed on thelower surface of the crystal piece 10E. In either case, the electrode54E may be electrically connected to the IC 200 via an electricallyconductive adhesive 49A, the conductive pattern 491 formed on the innersurface of the lower portion of the casing 30, and the wire 493.

The magnet 59E is provided such that the magnet 59E serves as a part ofthe lid 34E. The magnet 59E may be provided only in a region thatoverlaps the coil pattern portions 511E and 521E when viewed in a planview, for example. However, the magnet 59E may be provided such that themagnet 59E forms the entire lid 34, or may be formed by coating amagnetic flux generating material (e.g. magnetic material) on the lid34. The magnet 59E forms the magnetic flux passing through the center ofthe spiral pattern portion of the coil 50E when viewed in the Ydirection. The magnet 59E is provided such that the N pole and the Spole are positioned on the opposite ends in the Y direction, asillustrated schematically in FIG. 16. In the example illustrated in FIG.16, the magnet 59E has the “S” pole on the side which is not visible inFIG. 16; however, the N and S poles may be arranged in a reversedmanner. The magnet 59E may be provided at a position where the densityof the magnetic flux passing through the coil 50E is maximum in theneutral state (for example, in a state of not oscillating) of thecrystal piece 10.

In the example illustrated in FIGS. 14 to 16, the spiral pattern portionof the coil 50E are formed in a plurality of turns in order to increasethe number of windings, but may be wound once. Further, in the examplesillustrated in FIGS. 14 and 16, the coil pattern portions 511E and 521Eare provided on the farther side from the bank portion 31 in the Xdirection with respect to the excitation electrodes 20 (i.e., the freeend side of the crystal piece 10E); however, the coil pattern portions511 and 521 may be provided at an arbitrary position with respect to theexcitation electrodes 20. For example, the coil pattern portions 511Eand 521E may be provided on the side closer to the bank portion 31 inthe X direction with respect to the excitation electrodes 20.

Also, according to the third embodiment, the same effects as in thefirst embodiment can be obtained. It is noted that, in the thirdembodiment, it is possible to implement the modifications as describedabove and illustrated in FIGS. 10A to 10C. That is, in the thirdembodiment, the magnet 59E may be provided such that the magnet 59Eforms a part of the casing 30 (see FIG. 17A), may be provided in a formof a substrate (see FIG. 17B), or may be replaced with an electromagnet(see FIG. 10C).

For example, according to a crystal oscillator 100F illustrated in FIG.10A, a magnet 59F is provided such that the magnet 59F forms a part ofthe casing 30. The magnet 59F may be embedded in the casing 30, asillustrated in FIG. 10A. However, the magnet 59F may be also formed byapplying a magnetic flux generating material on the casing 30. It isnoted that the magnet 59F is provided such that the N pole and the Spole are positioned on the opposite ends in the Y direction, asillustrated schematically in FIG. 17A. In the example illustrated inFIG. 17A, the magnet 59F has the “S” pole on the side which is notvisible in FIG. 17A; however, the N and S poles may be arranged in areversed manner.

According to a crystal oscillator 100G illustrated in FIG. 17B, a magnet59G is provided such that the magnet 59G is parallel to the surface ofthe crystal piece 10E and does not contact the crystal piece 10E. Inthis case, the magnet 59G may be in a form of a substrate, or may beformed by applying a magnetic flux generating material to a substrate.Further, the magnet 59G may be supported by the crystal piece 10E or thecasing 30 by suitable support means (not illustrated). It is noted thatthe magnet 59G is provided such that the N pole and the S pole arepositioned on the opposite ends in the Y direction, as illustratedschematically in FIG. 17B. In the example illustrated in FIG. 17B, themagnet 59G has the “S” pole on the side which is not visible in FIG.17B; however, the N and S poles may be arranged in a reversed manner.

All examples and conditional language recited herein are intended forpedagogical purposes to aid the reader in understanding the inventionand the concepts contributed by the inventor to furthering the art, andare to be construed as being without limitation to such specificallyrecited examples and conditions, nor does the organization of suchexamples in the specification relate to a showing of the superiority andinferiority of the invention. Although the embodiment(s) of the presentinventions have been described in detail, it should be understood thatthe various changes, substitutions, and alterations could be made heretowithout departing from the spirit and scope of the invention. Further,all or part of the components of the embodiments described above can becombined.

What is claimed is:
 1. A crystal oscillator device, comprising: acasing; a crystal piece provided in the casing; a pair of excitationelectrodes provided on the crystal piece; a coil provided on the crystalpiece; a magnetic flux generating member configured to generate magneticflux passing through the coil; and an alarm generator configured togenerate an alarm based on a signal whose amplitude is equal to or lessthan a reference value, the signal being generated in the coil.
 2. Thecrystal oscillator device of claim 1, wherein the reference value isgreater than the amplitude that is obtained when an output of anoscillation circuit including the crystal piece stops.
 3. The crystaloscillator device of claim 1, further comprising: an inverting amplifierelectrically connected between the pair of excitation electrodes; and again control unit configured to increase a gain of the invertingamplifier when the amplitude becomes equal to or less than the referencevalue.
 4. The crystal oscillator device of claim 3, wherein theinverting amplifier includes an operational amplifier, a first resistor,and a second resistor, the second resistor having a resistance valuelarger than that of the first resistor; and the gain control unitswitches from a first state, in which an inverting terminal of theoperational amplifier is electrically connected to an output terminal ofthe operational amplifier via the first resistor, to a second state, inwhich the inverting terminal is electrically connected to the outputterminal via the second resistor, to increase the gain.
 5. The crystaloscillator device of claim 3, wherein the inverting amplifier, the alarmgenerator, and the gain control unit are provided in the casing.
 6. Thecrystal oscillator device of claim 1, wherein the magnetic fluxgenerating member is provided in the casing or on the casing.
 7. Thecrystal oscillator device of claim 1, wherein the magnetic fluxgenerating member is provided on the crystal piece or the casing suchthat a density of the magnetic flux passing through the coil changes dueto the oscillation of the crystal piece.
 8. The crystal oscillatordevice of claim 1, wherein the magnetic flux generating member includesa magnet.
 9. The crystal oscillator device of claim 1, wherein the coilincludes a coil pattern portion formed on the crystal piece.
 10. Thecrystal oscillator device of claim 9, wherein the coil pattern portionsare formed on opposite sides of the crystal piece, the opposite sidesbeing in a thickness direction of the crystal piece.
 11. The crystaloscillator device of claim 10, wherein the coil includes a through-holethat penetrates the crystal piece in the thickness direction thereof toelectrically connect the coil pattern portions.
 12. The crystaloscillator device of claim 10, wherein the crystal piece includes a slitthat penetrates the crystal piece in the thickness direction thereof,and the coil pattern portions on the opposite sides of the crystal pieceare electrically connected via the slit.
 13. The crystal oscillatordevice of claim 10, wherein the coil includes wiring portions extendingfrom centers of spiral patterns in the coil pattern portions on theopposite sides of the crystal piece to edge portions of the crystalpiece, the coil pattern portions on the opposite sides of the crystalpiece are electrically connected via the wiring portions, and insulatingportions are provided on the crystal piece, the insulating portionselectrically insulating the coil pattern portions from the wiringportions.
 14. A method of measuring a characteristic of a crystaloscillator, the method comprising measuring a characteristic of thecrystal oscillator based on a signal, the signal being generated in acoil provided on a crystal piece in a state in which magnetic fluxpassing through the coil is generated with a magnetic flux generatingmember and the crystal oscillator is in an oscillating state.
 15. Acrystal oscillator, comprising: a crystal piece; excitation electrodesprovided on the crystal piece; a coil provided on the crystal piece; anda magnetic flux generating member configured to generate magnetic fluxpassing through the coil.